The main aim in this research is to reach a better understanding of the effects of aging on central controls of body temperature. In one line of research the broad hypothesis is that some of the reduction in thermoregulation capacity and in febrile responses in aged homeotherms may be attributable to reduction in central sensitivity to pyrogens, local temperature and naturally occurring biological constituents of the brain. Concomitantly, these central temperature controls may become more sensitive to drugs commonly taken by elderly patients, which cause dysthermia. In another line of research the aim is to determine the degree to which aged animals are able to control body temperature and to develop fever after the primary central temperature control mechanism is destroyed. In all of the research either squirrel monkeys or rabbits of documented age are used. We hope to gain information about the effects of aging on central temperature controls which will form the basis for future clinical application and which will provide a model for the understanding of central control of other autonomic functions within the aged brain.